Bubble-up pump



y 19, 1964 J. VAN DER STER 3,133,507

BUBBLE-UP PUMP Filed Oct. 4, 1960 3 Sheets-Sheet 1 (max.-

INVENTOR 70- 5mm unmaoLl/l.

y 19, 1964 J. VAN DER STER 3,133,507

BUBBLE-UP PUMP Filed Oct. 4, 1960 3 Sheets-Sheet 3 FIG.5

INVENTOR XJW um n,

Evy ANT 2 a E VA United States Patent Ofi ice 3,133,507 Patented May 19, 1964 Bubble-up pumps are simple machines for lifting liquids comprising a short wide pipe referred to as fall pipe the lower end of which is in communication with a narrow riser or raising pipe to which thermal energy can be supplied at a point below the level of the liquid in the fall pipe so that in the riser pipe vapour bubbles are produced which raise the liquid in this pipe similarly to gas admitted to the lifting pipe of a so-called air-lift pump.

Such pumps are suitable inter alia for lifting liquid gases.

Extensive investigations have been performed on such bubble-up pumps particularly for lifting liquid air, nitrogen and oxygen.

It has been found that there is a value of the heat flux supplied to the pump at which the delivery of the pump is a maximum.

According to the present invention a heat flux 1 is supplied to the pump which at most is equal to the value of the heat flux at which the delivery of the pump is a maximum.

This step has several effects. The efficiency of the pump is improved. The pump is more readily controllable and it operates with satisfactory reproducibility. Furthermore the pump operates quietly. If the heat supplied exceeds the pump exhibits a spouting action similar to a fountain and this may be highly undesirable.

Applicant has also found a formula for expressed in Watts as a function of the inner diameter in cm. of the riser pipe and of the so-called raising ratio A of the pump. Surprisingly, this formula proves to hold within reasonable narrow limits not only for liquid air but also for liquid nitrogen and liquid oxygen.

Hence, according to the invention the amount of thermal energy which at most should be supplied to such a pump to ensure quiet operation can be accurately determined.

It has been found that in watts= The formula holds for d 1 cm. and for a pressure of 1 atm.

In this formula:

F=amount of liquid raised in cos/sec. =heat flux in watts (also referred to as heating energy).

A=raising ratio (explained more fully with reference to FIGURE 1 A=a loss term in cos/sec. which depends solely on the diameter of the raising pipe.

d=diameter of the riser pipe in cm.

When the pump is used under a pressure of p atm.,

must be substituted for p in the formula. From this formula it follows that the maximum delivery is equal to A It has been found that the loss term A depends solely on d. For d=0.3, 0.4, 0.5, 0.6, 0.8, and 1.0 cm., respectively, A is found to be 0.05, 0.4, 1.0, 1.7, 3.0 and 7.5 ccs./sec., respectively.

FIGURE 1 shows diagrammatically a bubble-up pump. Reference numeral 1 denotes a fall pipe, 2 a riser pipe and 3 the connection between the pipes 1 and 2. At Q thermal energy is supplied. I is the distance between the level in the fall pipe and the level of the point Q at which heat is supplied. I is the raising height.

Thus, it follows that r *2 FIGURE 2 is a graph representing the variation of F as a function of I fora pump in which d and A are constant.

The invention shows that the curve in FIGURE 2 has a maximum and that the heat supply I had better be less than and preferably less than 0.8 1% since this ensures quiet operation of the pump.

FIGURE 3 shows the variation of as a function of d and A.

FIGURE 4 shows the variation of F as a function Of d and A.

For d 1.0 cm. we have:

In most cases d should not exceed 0.6 cm. since the efliciency of the pump decreases with increase in the diameter.

The efliciency of the pump is highly dependent on A. Therefor A should be as high as possible. When A decreases, there follows a range in which the pump no longer operates. This range is found by making F equal to 0.

The result is shown in the graph of FIGURE 5.

It has been found that heating of the riser pipe must be effected through a zone H (FIGURE 1) having a surface area such that internally of the pipe the maximum heat flux per unit of the surface area does not exceed from 1 to 2 Watts sq. cm.

The preceding discussion permits of designing a bubbleup pump.

An example follows:

Liquid nitrogen must be raised in an amount of 25 litres/hour to a height of 1 meter. Hence, F :25 litres/ hour=7.0 cos/sec. and l cms. If it is assumed that the maximum immersion of the riser pipe is 40 cms. and that the centre Q (FIGURE 1) of the area at which heat is supplied lies 10 cms. above the lower end of the riser pipe, l =4010=30 cms. and hence According to FIGURE 5 this value of A is sufficient to design a bubble-up pump having a suitable diameter d.

Two cases can now be calculated:

Case 1 Case 2 Desired delivery of liquid. F=7.0 cos/see F=7.0 cos/sec. Diameter of the riser pipe. d=0.4 em d=0.6 cm. With A=0.3 it follows Fmnx=0.7 cos/sec. Fmax 1.5 cos/sec.

from Fig. 4. With A=0.3 it follows bmux=9.5 wattsnu- I mux=24 watts,

from Fig. 3. With F=0.8 Fm F=0.54 cos/see F=l.2 cos/sec.

7 T humber of pumps n 0.54 13 'n 6.

Heat flux per pump (cal- I =5.5 watts I =l7 watts.

eulated from the formula for F). Total heat flux I tm=72 watts.-. I mul=102 watts.

In most applications, d:0.6 cm. is to be preferred to d=0.4 cm., since at the lower value of d the riser pipe is more liable to be clogged by small pieces of ice.

FIGURE 6 shows the way in which a number of pumps A and B can be operated in series. A common outlet is designated 5.

A riser pipe 2 of a pump A delivers liquid to a fall pipe 1 of a pump B. Vapour from the riser pipe 2 is supplied through a pipe 6 to a vapour collecting chamber 7 of the pump B. A common vapour outlet is designated 8.

What is claimed is:

A vapor lift pump for liquid air comprising a fall pipe and a riser pipe, said riser pipe having a diameter not in excess of .6 cm., a connecting pipe connecting the bottom ends of said fall and riser pipes whereby said fall pipe and riser pipe communicate with each other, and an electric heating means surrounding said riser pipe and closely adjacent to the connecting pipe for supplying thermal energy over a predetermined zone of said riser pipe of such a surface area that internally of said riser pipe the maximum heat flux per unit of surface area does not exceed 2 Watts/ sq. cm., said heat flux being supplied to said riser pipe being at most equal in watts to of the value of it max. in which where d is the inner diameter in centimeters of the riser pipe of the vapor lift pump and A is the raising ratio of the pump.

References Cited in the file of this patent UNITED STATES PATENTS 

